The universal methodology for load balancing in the Web environment is the front-end load balancer (FE LB). This is a natural fit for HTTP transactions which are short-lived, non-real-time, and crowd-to-server. Some SBC application use cases are similar to the HTTP usage and, for these, a similar FE LB approach is applicable. The FE LB, however, is not a general solution to load balancing for a SBC service. To address the wider range of deployments, another system architecture calls for a Domain Name System (DNS)-based load balancing solution wherein a first stage of load-balancing occurs when the peers use DNS for resolution. This is followed by a second stage of load balancing with the elements of the SBC cluster internally retarget a portion of requests as necessary.
While the DNS based approach is generic and widely applicable, it is not ideal. The use of DNS mapping to individual SBC addresses has several disadvantages. First, it requires that the peers use RFC 3263 style DNS resolution for SIP services. While this support is widespread, it is not universal in all networks. Second, it does not provide a single IP address appearance for signaling since DNS is resolved to the individual server addresses. And third, it complicates horizontal scaling as the DNS infrastructure has to be updated when SBC instances are added or removed.